After repeated warnings and fines from agencies like the Occupational Safety and Health Administration (OSHA), do companies strive to get better or do they fall back into old habits? That is why there has to be a better way to study how to keep the workplace safe.

As it turns out, random safety inspections do improve safety without leading to burdensome expense or job loss.

Most workplace inspections come via the U.S. Occupational Safety and Health Administration (OSHA), a federal agency tasked with setting and enforcing safety standards, or by state agencies approved by OSHA. But the efficacy of these inspections is difficult to study in an unbiased way, said Michael Toffel, an environmental management expert at Harvard Business School. Most safety regulators don’t inspect companies at random and instead typically focus on those that have accidents or where workers have filed complaints. Afterward, injury rates tend to revert back to whatever they were before the incident occurred, even without an OSHA inspection. So researchers could think the inspection played a bigger role in the reduction of injuries than it actually did.

On the other hand, if OSHA finds incomplete documentation during an inspection, it will require the company to keep better records, which could then lead to more reported injuries, Toffel said. A study of these sites would make it look as if the inspection led to an uptick in injuries.

A more objective picture came courtesy of California’s Division of Occupational Safety and Health, which carries out some of their inspections on workplaces selected at random. With economists David Levine of the University of California, Berkeley, and Matthew Johnson of Boston University, Toffel looked for workplaces inspected between 1996 and 2006 for which they could find similar companies eligible for inspection but had not yet gone through the process. They ended up with 409 matched pairs of inspected and uninspected workplaces. The researchers used workers’ compensation claims over the period ranging from 4 years before through 4 years after the inspection to determine illness and injury rates. They also examined injuries during the same block of time for the companies that did not undergo inspection. Companies included in the study produced “fabricated metal” (doors, car parts, aerospace products), wood, or food products.

Comparing the workplaces randomly chosen for inspection with matched “controls, which is comparable to using a placebo group in a trial of a new drug or vaccine, had never been done before, Toffel said.

Companies undergoing random inspections saw workplace injuries decline by about nine percent in the four years following the date of inspection compared with injury reports during the same time period in firms not inspected, the researchers said. The cost of the injuries reported, including medical treatment and missed work, fell by 26 percent. Using information from financial data provider Standard & Poor’s, the investigators found the inspections had no effect on employment, total earnings, sales, or the survival of the company.

“Our study suggests that randomized inspections work as they’re meant to, improving safety while not undermining the company’s ability to do business,” Toffel said. “Now we’d like to get more data to see exactly how inspections reduce injuries, and to investigate what kinds of companies would get the most or least benefit from safety regulation.”